BAGHDAD
— In April, with anger swelling at the US occupation and a Marine-led assault on the Sunni city of Fallujah,thousands of Shiites provided assistance to their Iraqi brothers in the city.

Adnan Feisal Muthar filled up his truck with food and drove it to Fallujah to help residents rendered homeless by US bombing. His uncle and two of his sons donated blood for the wounded. "We wanted to help the people there,'' says Mr. Muthar. "They were Iraqis and they were suffering."

But the city west of Baghdad is no longer a sympathetic rallying place for a unified Iraqi resistance. It is now seen as run by intolerant and exclusivist Sunni imams who are seeking to turn it into a haven for Al Qaeda ideologues. Fallujah is emerging as a symbol of the disparate nature of the overall insurgency inside Iraq. Many Shiites, like the Muthars, have stopped supporting it.

Since two of Muthar's brothers and four of his cousins - all members in a family trucking cooperative - were tortured and murdered in the resistance stronghold three weeks ago, he's changed his mind about how the US handled Fallujah.

"They should have done whatever it took to take that place over,'' Muthar says. "It's been left in the hands of people who call themselves Muslims but they're not. They're simply inhuman."

The killingsand mutilations of the six truckers (some could only be identified by family members from old scars) have shaken many Iraqis. While some Iraqis had mixed feelings about the similar killing and mutilation of four US security contractors, in April, these latest murders have inflamed the Shiite community here, and alienated others.

"It makes me very uncomfortable to say this, but if the American's weren't around [to attack] we would be fighting among ourselves,'' says a young native of Fallujah who participated in attacks against US forces last year but has since quit the resistance, saying he's been disillusioned by a disregard for civilians shown by some insurgents.

He was particularly disturbed by the mutilation of the Shiite truck drivers. "We can't be satisfied with this new group - they execute alleged spies in the streets without any evidence at all, sometimes it's just payback for a personal dispute. Those Shia were innocent men."

A deeply religious Muslim himself, he says fighters inside Fallujah are now badly split between people like himself who were opposed to the occupation on nationalist grounds and what he calls "extremist Salafys," the catchall term used for the branch of Islam espoused by Al Qaeda and most in Saudi Arabia.

He says most of the men in the movement are Fallujah locals, but he says small pockets of Saudis, Syrians, and Yemenis fight with them. US and Iraqi officials believe that Abu Musab Zarqawi, a Jordanian militant with ties to Al Qaeda, has made the city a base of operations.

"It's like the ghost of the Baath is hunting us down. These guys who used to serve Saddam have grown long beards and wear skullcaps and say they want an Islamic state,'' he says. "In April we were all struggling side by side, but now it's about their own political interests."

Who precisely gave the order for the Shiites' abduction and murder isn't yet clear. The city is controlled by Sheikh Abdallah al-Janabi and his deputy, Dhafer Al-Obeidi, the head of the Hadra al-Muhammadiyah mosque. Mr. Obeidi - who sometimes also goes by the name Dulaimi - was delegated by Sheikh Janabi to run the city's after the US Marines withdrew in April.

The US left Fallujah's security in the hands of local cops and a special Iraqi military unit the US created in April. But sources in the city say the police and the brigade take their orders from insurgent groups, or at best just stay out of their way.

The six Shiites were killed about a week after their abduction on June 5, the details of which have been provided to the family by Mohammed Khudier, a 12-year-old cousin of Adnan Feisal Muthar. Mohammed was riding with another cousin, 18-year-old Ahmed Ali Hilal, to start learning the ropes of the family business. Mohammed, later released because of his youth, was the only survivor.

After dropping a load of tents at a camp for the new Iraqi National Guard on the outskirts of the city, their truck was ambushed. They survived and went to the police to find safe passage out of the town. The police took the men to see Obeidi at the Muhammadiyah mosque.

"They were taken in convoy there, with police cars front in back,'' says Adnan Muthar. "Janabi is like the prince of that town now." Over the next week, the family made increasingly frantic appeals to Mr. Obeidi and Sheikh Janabi for the men's release.

Mr. Muthar says Sheikh Janabi told them that the men were being interrogated, and that their release could be obtained for a ransom. But in the end the family was told it could collect their bodies. Two of those killed were Adnan's brother, Hamid Feisal Mutha and his adopted brother Khalid Latief Muthar, who had five young children between them.

Sitting in the family home in Sadr City, Adnan and his morose father, Sheikh Feisal Muthar, urge their visitors to look at pictures that showed the extent of men's torture. They point to were a tattoo that said "Imam Ali" was sliced out of Hamid's arm, saying it was evidence of the sectarian nature of the crime. Shiites revere Ali, a descendant of the prophet Mohammed, while extremist Sunnis attack the practice as polytheistic. "Janabi was responsible for this, and we want justice,'' says Adnan.

Shortly before the US occupation authority was dissolved on June 28, Ambassador Paul Bremer issued arrest warrants for Sheikh Janabi and Obeidi, but no action has been taken by Iraqi authorities. In an interview with the Al Arabiya satellite channel, Sheikh Janabi said he had nothing to do with the murders.

Officials at the Iraqi Ministry of Interior say they're mulling terms of an amnesty for Iraq's insurgents. "We are having a dialogue with some of the important figures in Fallujah,'' says Interior Minister Falah Hassan al-Nagib. "We know there are some splits in the city. We think that most of the trouble is being created by foreigners there."

Nonetheless, other interior ministry officials say the overwhelming majority of fighters in their custody are Iraqis, including four men held for with beheading American Nicholas Berg in May.

US and Iraqi officials say Fallujah has become a haven for the country's tiny cohort of foreign fighters, and it's turning out local Iraqis committed to establishing an Islamic state. While the popularity of such views is limited, having established a beachhead with relative impunity has strengthened their movement.